The present invention refers to an extra short transmission shaft.
Conventional transmission shafts normally comprise a tubular section and a solid bar telescopically fitted into the tubular section. Longitudinal flutes or teeth are machined in part of the extension of the solid bar, which cooperate or mesh with corresponding flutes or teeth machined on the inner surface of the tubular section so as to permit relative longitudinal movement therebetween while ensuring transmission of rotary movements.
Respective coupling forks are connected to the free ends both of the tubular section and of the solid bar, the forks being solid and dimensioned to be sufficiently robust to support forces and stresses developed during use. They are thus relatively large and heavy.
The coupling forks are connected at their free ends to respective coupling flanges or forks by means of interposed crossheads that are articulated about orthogonal gudgeon pins so as to form a cardan.
One of the coupling flanges may be coupled to a drive shaft component whereas the other may be connected to a driven component, such as a differential, to permit the transmission of power and torque.
Such coupling devices are used to connect nonaligned intercepting axles or shafts, that is to say, shafts being permanenty angled with respect to each other.
Shafts in general are forced to undergo continuous stress inversions which, within a relatively short period of use, may lead to sudden rupture due to fatigue. Apart from this, extreme pressure is applied to the bearings which causes overheating and sometimes more serious problems.
Problems of such a nature that are found in the above type of mechanism are caused, amongst others, by differences of level between the drive and driven components due to the small axial relative movement between the sections of the transmssion shaft, as well as to the development of elevated torsional stresses therebetween concentrated over the small area of contact between the torque transmitting flutes or teeth.
In view of such elevated torque in a relatively small contact area, that is to say, the surfaces of relative movement of the flutes or teeth on the tubular sections, the specific pressure on the flanks of the teeth frequently attains such a magnitude that, instead of sliding, the flanks become rigid and jam whereby the shaft sections begin to shift together as a single part and transmit such movement also to the drive component, for example, the engine which is supported on mounting blocks. This movement causes mechanical misadjustments that produce trepidations, vibrations and irregularities in the acceleration control of the engine.
Many studies have been made with a view to diminish or even eliminate the friction--and the consequent jamming--between the teeth of the transmission shaft sections. However, up to the moment satisfactory results have not been achieved.